Preheat the oven to 425. Press one of the pie crusts into a 9-inch deep dish pie pan.

In a bowl combine the flour and sugar and mix to combine. Add the beaten egg and raspberry and blueberries. Mix to combine and then add the rhubarb and mix thoroughly. Spoon the mixture the pie crust. Top the fruit with the remaining crust, and crimp around the edges to seal. Using a sharp knife or a fork poke vent holes in the top crust (at least 5 or 6). Bake for 10 minutes then reduce the heat to 350 and bake for 30 to 35 more minutes. Remove from the oven and cool for at least 30 minutes before serving.